1. Field of Invention
This invention relates to spindle assemblies and more particularly to a new and improved spindle assembly especially suited for reducing non repetitive runout (wobble) in a magnetic disc storage system.
2. Description of the Prior Art
A spindle assembly of a magnetic disc storage system has typically comprised a vertically oriented shaft rotatably supported by a pair of ball bearings disposed along the shaft within the bore of a support housing. A somewhat bell shaped hub adapted to support magnetic discs is affixed to the shaft for rotation therewith after the shaft is supported with in the housing. The hub is attached to the shaft near the end above the upper ball bearing such that the sides of the hub extend downward outside the shaft housing to accommodate the magnetic discs in a vertically stacked array slightly spaced relative to one another and concentrically disposed about the hub and shaft. Mechanical tolerances of the ball bearings, the housing bore and the shaft diameter and circumference result in a nonrepetitive runout or wobble condition which causes any point on a magnetic disc to move in slightly varying circles on successive rotations. The condition is aggravated in magnetic discs located near the lower extremity of the hub due to the fact that such portion of the hub is less rigid and more likely to introduce additional wobble.
A more recently contrived spindle assembly which has been used in the magnetic disc storage art comprises a horizontally oriented shaft rotatably supported by a pair of ball bearings disposed along the shaft within the bore of a support housing. The hub that supports the discs is essentially a collar which is attached to the shaft in the region intermediate the ball bearings. Such construction will considerably reduce nonrepetitive runout compared to the aforedescribed devices, in which the hub is supported on the shaft at one end outside the region between the bearings, provided that the centerline of the housing bore is aligned collinearly with the longitudinal axis of the shaft. This alignment is difficult to achieve, however, because the housing is made in two pieces each of which has an end of the shaft inserted thereinto after the hub and discs have been mounted on the shaft.
The foregoing limitations of presently available magnetic disc storage spindle assemblies are overcome to a great extent by means of apparatus constructed in accordance with the principles of the present invention as will become apparent from the ensuing description.